From e4a6b84962cc2fb4f4b8bb532a84bab5bfd68d99 Mon Sep 17 00:00:00 2001 From: Alessandro Arzilli Date: Tue, 4 Jan 2022 15:47:02 +0100 Subject: debug/elf: do not read unrelated bytes for SHT_NOBITS sections SHT_NOBITS sections do not occupy space in the file and their offset is "conceptual", reading their data should return all zeroes instead of reading bytes from the section that follows them. Change-Id: Iaa9634792c1909c3e87dab841dd646cd6dcf9027 Reviewed-on: https://go-review.googlesource.com/c/go/+/375216 Reviewed-by: Emmanuel Odeke Run-TryBot: Emmanuel Odeke TryBot-Result: Gopher Robot Reviewed-by: Ian Lance Taylor --- src/debug/elf/elf_test.go | 22 ++++++++++++++++++++++ src/debug/elf/file.go | 12 ++++++++++++ 2 files changed, 34 insertions(+) diff --git a/src/debug/elf/elf_test.go b/src/debug/elf/elf_test.go index a61b491090d..b8c310dba55 100644 --- a/src/debug/elf/elf_test.go +++ b/src/debug/elf/elf_test.go @@ -47,3 +47,25 @@ func TestNames(t *testing.T) { } } } + +func TestNobitsSection(t *testing.T) { + const testdata = "testdata/gcc-amd64-linux-exec" + f, err := Open(testdata) + if err != nil { + t.Fatalf("could not read %s: %v", testdata, err) + } + defer f.Close() + bss := f.Section(".bss") + bssData, err := bss.Data() + if err != nil { + t.Fatalf("error reading .bss section: %v", err) + } + if g, w := uint64(len(bssData)), bss.Size; g != w { + t.Errorf(".bss section length mismatch: got %d, want %d", g, w) + } + for i := range bssData { + if bssData[i] != 0 { + t.Fatalf("unexpected non-zero byte at offset %d: %#x", i, bssData[i]) + } + } +} diff --git a/src/debug/elf/file.go b/src/debug/elf/file.go index eefcaab8d69..8c84661c5f7 100644 --- a/src/debug/elf/file.go +++ b/src/debug/elf/file.go @@ -120,6 +120,9 @@ func (f *File) stringTable(link uint32) ([]byte, error) { // Even if the section is stored compressed in the ELF file, // the ReadSeeker reads uncompressed data. func (s *Section) Open() io.ReadSeeker { + if s.Type == SHT_NOBITS { + return io.NewSectionReader(&zeroReader{}, 0, int64(s.Size)) + } if s.Flags&SHF_COMPRESSED == 0 { return io.NewSectionReader(s.sr, 0, 1<<63-1) } @@ -1453,3 +1456,12 @@ func (f *File) DynString(tag DynTag) ([]string, error) { } return all, nil } + +type zeroReader struct{} + +func (*zeroReader) ReadAt(p []byte, off int64) (n int, err error) { + for i := range p { + p[i] = 0 + } + return len(p), nil +} -- cgit v1.2.3-54-g00ecf